An industrial robot is an electro-mechanical machine that is controlled by a computer program, electronic circuits, or both. The industrial robot may be either stationary or mobile (e.g., capable of navigating from one location to another location). For example, the industrial robot may have wheels (or another form of conveyance) to enable the industrial robot to navigate to different locations. Industrial robots that can navigate independently of each other may be referred to as mobile drive units (MDUs). The MDUs may be capable of performing activities using one or more arm-like mechanisms to grasp an item, release the item, etc. Based on the type of task that is to be performed, two or more MDUs may coordinate their respective activities to perform a task.
In an area (e.g., a factory, a warehouse, a materials handling facility or similar type of setting) where multiple MDUs are performing activities, under some circumstances, humans may enter the area. For example, plastic wrap used to cover a load of items may foul the wheels of an MDU. As another example, an item from the load of items may fall and obstruct the path of an MDU or partially damage an MDU. Under such circumstances, a human may enter the area to perform an activity such as removing the plastic wrap from the wheels of the MDU, removing an item obstructing the path of the MDU, or repairing the MDU. The MDUs may be instructed to perform one or more activities, such as transporting items between locations in a materials handling facility, transporting a shelving unit from one location to another, docking with a charging unit, handing off a trash container to a dumper unit, etc. When a human enters an area in which multiple MDUs have been instructed to perform one or more activities, the human may risk being inadvertently injured by one or more of the MDUs as the MDUs perform their activities.